The present invention relates to an occupant position sensing system and more particularly to an ultrasonic sensing system.
Ultrasonic sensors have been used for proximity or distance measurement. These devices typically transmit a short burst of ultrasonic sound toward a target which reflects the sound back to the sensor. The system then measures the time for the echo to return to the sensor and computes the distance to the target using the speed of sound in the medium. In the context of a safety restraint system, this medium is air. To accurately use the echo as a measurement of distance, various environmental and operating parameters need to be taken into account or chosen carefully. As an example, the speed of sound in air will vary as a function of temperature. It is also known that the wavelength of sound changes as a function of both speed of sound and the frequency. There are also various attenuation factors such as the reduction of the amplitude of the sound wave due to humidity. Other factors in inaccuracies will enter the system due to background noise.
The object the present invention is to design a position sensor that will operate adequately in an acoustically and mechanically noisy environment such as the environment that will be found within the passenger compartment of a vehicle. It is an object of the present invention to provide a method of detection and tracking of an occupant's position in a crash utilizing ultrasonic technology. The ultrasonic transducer will be used in what is called a "smart occupant restraint system." These types of systems have been proposed in the art. Such systems are developed to control safety restraint devices such as the activation of an air bag during a crash in a way to provide more protection to the occupant. Typically when a crash occurs, a control device receives a signal emanating from a crash sensor indicating that a crash has occurred. Various sensors positioned about the passenger compartment are utilized to define the size and position of an occupant and these parameters are used by the controller to determine how best to operate the safety restraint devices. One of the critical elements in operating a smart occupant restraint system is to be able to determine accurately the position of a vehicle occupant relative to an air bag door, that is, the location of the non-activated air bag.
Accordingly the invention comprises an occupant position measuring system comprising: transmitter means for generating a pulse modulated transmitter signal; receiver means for receiving a reflection of the transmitter signal, the receiver means being characterized as having a relatively low Q factor; control means, responsive to the receipt of the reflected signal and for generating an indication of the distance between an occupant and the receiver means. The transmitter means may also preferably be of a low Q factor.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.